There has been great need in the window industry for window construction of the type that secures a movable window sash into an air and water sealed engagement with the outer window frame. Present construction of windows having a movable or slidable vent window for use in residential and commercial buildings attempt to seal the vent window in the window frame by means of placing weatherproofing strips in the vent window frame or in the outer window frame. This type of construction suffers from many problems in that the weatherproofing strips between the window frame and the vent window are constantly engaged which tends to wear the weatherproof stripping as the vent window is operated through a plurality of openings and closings. Further, in present day construction, lightweight aluminum is used in the vent window frame surrounding the vent window pane which engages the weatherproofing strips, or has weatherproofing strips attached to it engaging the window frame, and as a result of the use of lightweight metal, the metal is subject to warping from the constant pressure placed on it by the window frame and weather stripping, regardless of the window position. The tendency then is for the vent window to warp away from the window frame and thus no longer maintain the sealed relationship.
There have also been many attempts in the past to provide sealing means and manners between the frame of the vent window and the window frame, one example being a window construction having cables engaging the periphery of the vent window frame combined with mechanical linkage to seal the vent window frame to the window frame. In addition, there have been other complicated means to seal the vent window to the window frame, as for example shown in Coller, U.S. Pat. No. 3,225,393.